Definition
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Psoriasis: chronic, immune-mediated inflammatory skin disorder characterized by well-demarcated, erythematous plaques with silvery scales.
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Commonly involves extensor surfaces, scalp, and sacral region.
Epidemiology & Risk Factors
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Prevalence: 2–3% worldwide.
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Can affect any age; peak onset: 20–30 and 50–60 years.
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Triggers: trauma (Koebner phenomenon), infection (streptococcal pharyngitis → guttate psoriasis), stress, drugs (β-blockers, lithium, antimalarials, NSAIDs).
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Genetic predisposition: HLA-Cw6 association.
Types of Psoriasis
| Type | Features | Key Points |
|---|---|---|
| Plaque (Psoriasis vulgaris) | Most common, well-demarcated erythematous plaques with silvery scales | Extensor surfaces, scalp |
| Guttate | Small drop-like lesions | Often post-streptococcal; acute onset |
| Inverse | Smooth, red plaques in flexures | Less scaling; intertriginous areas |
| Pustular | Sterile pustules on erythematous base | Can be generalized or localized; may be severe |
| Erythrodermic | Widespread redness >90% BSA | Life-threatening; risk of fluid/electrolyte loss |
💡 High-Yield PLAB Tip:
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Guttate psoriasis = classic post-streptococcal trigger in children/young adults.
Clinical Features
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Well-demarcated erythematous plaques with silvery scales.
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Auspitz sign: pinpoint bleeding when scales removed.
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Koebner phenomenon: lesions appear at sites of trauma.
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Nail involvement: pitting, onycholysis, subungual hyperkeratosis.
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Pruritus variable.
Associated Conditions
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Psoriatic arthritis (10–30% of patients).
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Metabolic syndrome: obesity, diabetes, dyslipidaemia.
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Cardiovascular disease.
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Depression and psychosocial impact.
Investigations
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Usually clinical diagnosis.
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Skin biopsy only if atypical features or diagnosis uncertain.
Management
Topical Therapy (mild-moderate)
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Emollients – first-line adjunct.
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Topical corticosteroids – mainstay.
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Vitamin D analogues (calcipotriol) ± steroid combination.
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Coal tar, salicylic acid for thick plaques.
Systemic Therapy (moderate-severe or resistant)
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Methotrexate – immunosuppressive, weekly oral or IM.
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Cyclosporine – rapid action, nephrotoxicity risk.
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Acitretin – for pustular or erythrodermic psoriasis.
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Biologics – adalimumab, etanercept, secukinumab (specialist use).
Phototherapy
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Narrowband UVB therapy for moderate disease.
Complications
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Psoriatic arthritis → joint deformity.
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Erythrodermic psoriasis → fluid loss, infection risk.
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Psychological distress.
PLAB-Style Questions
Q1: A 22-year-old man develops multiple small, red, drop-like lesions on his trunk and limbs 2 weeks after a sore throat. What is the most likely type of psoriasis?
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A. Plaque psoriasis
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B. Guttate psoriasis
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C. Inverse psoriasis
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D. Pustular psoriasis
✅ Answer: B. Guttate psoriasis
(Post-streptococcal acute onset of small drop-like lesions is classic.)
Q2: A 45-year-old woman presents with well-demarcated, silvery-scaled plaques on the extensor surfaces of her elbows and knees. Nail pitting is present. She has joint stiffness in the morning. Which is the most important associated condition to assess for?
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A. Rheumatoid arthritis
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B. Psoriatic arthritis
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C. Osteoarthritis
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D. Gout
✅ Answer: B. Psoriatic arthritis
(Joint involvement with psoriasis is highly suggestive of psoriatic arthritis.)
High-Yield Pearls
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Plaques + silvery scales = plaque psoriasis (most common).
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Auspitz sign = pinpoint bleeding when scale removed.
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Koebner phenomenon = lesions at sites of trauma.
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Guttate psoriasis = post-streptococcal, acute onset.
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Always screen for psoriatic arthritis in patients with joint symptoms.
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Systemic therapy reserved for moderate-severe disease.
